Among the recent developments in electronic technology have been a number of electronic measuring systems capable of providing a digital indication representative of a value to be measured. Many of such systems respond to central sequencers to rapidly provide a plurality of measurements within a very short time so that a relatively accurate measurement indication is obtained. Other systems are capable of combining indications from a number of successive measuring operations to indicate comparative values obtained from successive measurements.
Generally, electronic measuring systems operate from an A.C. power supply and are not adapted for use with a portable instrument. Those systems which do operate from battery power, such as systems for vehicular use, are generally simple systems which do not have the capabilities of the more complex, non-portable measuring units. However, there is an increasing demand for electronic measuring units for portable or vehicular use, and particularly for electronic weighing units, such as that disclosed in U.S. Pat. No. 3,650,340 to R. S. Bradley, which may be used in agricultural and similar vehicles. Presently known portable and vehicular weighing systems of the electronic type which operate from battery power generally require an excessive warm-up period and must be deactivated during brief intervals of non use to prevent excessive battery drain. This is due to the fact that such systems draw constant power from the battery supply source.
All electronic measuring systems are subject to drift variations due to temperature, electrical characteristics, mechanical, environmental, and other effects inherent in such systems. In the more complex electronic measuring systems, such as that disclosed by U.S. Pat. No. 3,665,169 to Henderson et al, sophisticated automatic zeroing assemblies are employed to very accurately track zero in the system and compensate for drift. In less sophisticated electronic systems suitable for use in portable instrumentation, drift compensation is often nonexistent.
Conventionally, the more complex electronic measuring systems include indicator control units for indicator systems which are adapted to accomplish rounding of the output indication, the use of dividers for a digital measurement signal to provide signal ranging, and the use of up-down counters to arithmetically compute the value of an output indication. For example, the Henderson et al patent previously identified discloses both rounding of the output indication and the use of a counter system to compute the net weight sensed by an electronic weighing system. Although this net weight computation accomplished by the Henderson et al system does not employ up-down counters, the equivalent of up-down counter operation is provided by presetting the complement of a tare value into a counter system and subsequently counting out this tare value with a gross weight to achieve a net weight indication.
Similarly, the use of up-down counters in an electronic weighing system to count out a preset tare and to then provide a net weight indication from a gross weight input is disclosed by U.S. Pat. Nos. 3,788,410 to Allenspach et al and 3,777,828 to Dietemeyer. Both of these patented systems employ conventional absolute value indicating up-down counters of the type shown By U.S. Pat. Nos. 2,970,759 to Lanning, 3,159,792 to Metz, and 3,272,971 to Klenikowski. The absolute value up-down counter is particularly well adapted for tare calculations in an electronic weighing system, for such counters are designed to count toward zero in response to pulses in an input pulse train for counting the counter down from an initial count toward zero or a predetermined minimum count. When the counter registers zero or the minimum count, this condition is sensed and the counter is caused to count up from zero or the minimum count with any remaining pulses in the input pulse train.
The use of a divider stage between a counter and indicator system and an analog to digital conversion system is illustrated by U.S. Pat. No. 3,258,764 to Muniz et al. This divider stage may be employed to divide the pulse output from the measuring system down to a range acceptable in a counter and indicator assembly for the system. Should it become desirable to selectively vary the range of the weighing system by a predetermined factor, a variable divider of the type shown by U.S. Pat. No. 3,147,442 to Fritzsche et al is used.
Ideally, an electronic system employed in a small or portable measuring unit for weighing or similar applications should incorporate the features conventional to the more complex electronic measuring systems.
It is the primary object of the present invention to provide a novel and improved electronic measuring system adapted to provide a measurement signal which is the result of a plurality of measurement samples.
Another object of the present invention is to provide a novel and improved electronic measuring system which provides a measurement indication which is the result of a plurality of measurement samples which have been stored and filtered.
A further object of the present invention is to provide a novel and improved electronic measuring system incorporating a power supply unit which provides pulsed power to a transducer for the system.
Another object of the present invention is to provide a novel and improved electronic measuring system incorporating a power supply which provides pulsed power to a transducer for the system and a drift compensation unit which operates during intervals between said transducer power pulses to sense system drift.
Another object of the present invention is to provide a novel and improved electronic measuring system which includes an instability sensing assembly responsive to an unstable input measurement signal for preventing measurement during the period of instability.
A further object of the present invention is to provide a novel and improved electronic measuring system which includes a programmable low pass filter operable to pass the resultant output produced by a plurality of measurement samples stored in a sample and hold circuit.
Another object of the present invention is to provide a novel and improved electronic measuring system which includes a divider counter network in combination with an indicator assembly to increase the resolution of the indications displayed.
A further object of the present invention is to provide a novel and improved electronic measuring system incorporating an indicator system adapted to accomplish tare compensation, output indication round off and the comparison of successive measurements.
A still further object of the present invention is to provide a novel and improved electronic measuring system adapted to round off an output indication by ones, twos, or fives and to automatically sense whether a round off in fives should be up or down.